Brake pad with a wear indicator

ABSTRACT

The invention relates to a brake pad (1) having a wear indicator (5). The brake pad (1) has a first bore (20) opening out into the braking face (4) of the friction lining (2), a second bore (22) opening out into the first bore (20) and into the edge (23) of the lining, and a slot (24) which extends between the first bore (20), the second bore (22), the edge (23), and the braking face (4). The indicator (5) comprises a pellet (6) adapted to the first bore (20), a sleeve (14) slidably mounted on the conductors (12a, 12b) of the indicator (5) and urged against the pellet (6) by a resilient sheath (16) that bears against the connection terminal (15) of the indicator (5). The diameter of the sleeve (14) is substantially equal to the diameter of the second bore (22). The slot (24) serves to pass the conductor wires (12a, 12b) during installation of the indicator (5) on the brake pad (1), after the sleeve (14) has been moved away from the pellet (6).

The present invention relates to a brake pad for a vehicle brake, thepad comprising a friction lining and a wear indicator fixed thereto,said indicator comprising a body of insulating material and anelectrical conductor designed to be connected to an electrical indicatorcircuit, a portion of said conductor being disposed in said body in sucha manner that it is itself worn by a rotary part of the brake once thefriction lining has been reduced to a thickness of less than apredetermined value.

Brake pads are often fitted with indicators that are insulated fromground. Such indicators cause a warning light on the dashboard of thevehicle to light up as soon as they come into contact with the disk orrotary part that is connected tog round.

In general, the body of a wear indicator comprises a stud that ispluggable in an opening formed in a support plate for the frictionlining in a region that has no lining, either via the face that facesthe rotary part, or else via the opposite face. The state of the art isillustrated by FR-A-2,385,950, FR-A-2,513,716, FR-A-2,567,601,FR-A-2,647,868 and FR-A-2,619,348. Under such circumstances it isnecessary to provide means for preventing axial displacement of thestud; either flanges or snap-fastening means.

A wear indicator is also known from FR-A-2,465,924 in which the body isapplied to the support plate for the friction lining.

U.S. Pat. No. 3,967,167 provides for the wear indicator being receivedin a hole opening out to that face of the lining support which is remotefrom the rotary part and for the indicator to be held therein by awedging plate which is snap-fastened on said support face.

All of those devices require either indicator bodies that are complex inshape, or else additional parts that serve to hold the indicator on thebrake pad. In addition, installing such elements is complicated andrequires special tools, and dismounting the indicator is difficult oreven impossible.

Wear indicators are also known that are fixed into the friction liningby means of adhesive. However, such indicators are subjected to hightemperatures during braking. Such increases in temperature can loosenthe indicator relative to the lining. In addition, once an indicator hasbeen fixed in this way, it cannot be recycled when changing the brakepads of the vehicle, even if it has not itself been worn.

An object of the present invention is to provide a brake pad of Theabove-mentioned type in which it is easy to install the indicator.

According to the invention, the proposed brake pad is characterised bythe fact that the body is shaped to be received in the bottom of a firstblind bore formed in,he friction lining and opening out into the brakingface of said lining, by the fact that the means for fixing the indicatoron said lining comprise a rigid sleeve slidably mounted on theelectrical conductor in the vicinity of said body and suitable for beingreceived in a second bore formed in said lining and opening out intosaid first bore and to one of the edges of the lining, and by the factthat a slot is provided in the friction lining to pass the electricalconductor during installation of the wear indicator on said lining, saidslot being narrower than the diameter of the sleeve and extendingbetween said first bore, said second bore, said edge, and said brakingface.

Because of this disposition, the wear indicator is installed withoutusing a tool and without using adhesive, it suffices to move the sleeveaway from the body, and to slide the body into the first bore, whilepassing the conductor via the slot. Once the body reaches the end of thefirst bore, the conductor is centered in the second bore and it sufficesto move the sleeve back toward the body, causing it to penetrate intothe second bore. This locks the body in the end of the first bore.Removal of the indicator is performed in the reverse order. The sleeveis caused to slide along the conductor until it comes out from thesecond bore, after which the body is removed from the first bore, bycausing the conductor to pass though the slot. In the event of the bodybeing worn by the rotary part, the body is held in the end of the firstbore. This makes it possible to guarantee that the warning signalfunctions when the friction lining reaches a specified thickness that isless than a predetermined value.

Advantageously, means are provided for holding the sleeve in the secondbore. These means comprise a resilient sheath suitable for sliding onthe electrical conductor and exerting via one of its ends, a force onthe sleeve. This force is directed towards the body and the other end ofthe sheath bears against the plug fitted to the conductor for thepurpose of connection to the electrical circuit of the indicator.

The body of the indicator is advantageously in the form of a pellet. Ina preferred embodiment, the pellet includes an annular groove in itsperiphery and the electrical conductor is an insulated conductor wirehaving a loop received in the groove.

Other advantages and characteristics of the invention appear on readingthe following description given by way of example and made withreference to the accompanying drawings, in which:

FIG. 1 is a view of a brake pad showing the braking face that isintended to co-operate with a rotary part;

FIG. 2 is a plan view of the FIG. 1 brake pad as seen in the directionof arrow A in FIG. 1;

FIG. 3 is a section on a larger scale on line III--III of FIG. 4 showingthe wear indicator of the invention adapted to the brake pad of FIG. 1;

FIG. 4 is a section on a larger scale on line IV--IV of FIG. 3, showingthe wear indicator of the invention;

FIGS. 5A, 5B and 5C show different stages in installing the wearindicator of FIGS. 3 and 4 on the brake pad of FIGS. 1 and 2; and

FIG. 6 is a perspective view showing a variant embodiment of the wearindicator of the invention.

In the drawings, reference 1 designates a brake pad for a disk brake,the pad comprising a friction lining 2 mounted on a support plate 3. Thelining 2 has a braking face 4 that is designed to co-operate by frictionwith a disk that is associated with a wheel axle of a vehicle. The brakepad is fitted with a wear indicator 5 which is described in detailbelow.

As can be seen in FIGS. 3 and 4, the wear indicator 5 comprises a bodyconstituted by a pellet 6 of insulating material having a groove 8 inits periphery 7 in which a loop 9 of an insulated conductor wire 10 isreceived.

In the zone 11 of the pellet 6, from which two lengths of wire 12a and12b project, extending the loop 9, there is provided a recess 13 for apurpose that is explained below.

In the vicinity of this zone 11, a rigid sleeve 14 is provided which iscapable of sliding over the lengths of wire 12a and 12b. The ends of thelengths of wire 12a and 12b are fixed to as plug 15 for the purpose ofconnecting the conductor wire 10 to an electrical circuit for indicatingwear of the lining 2, said indicator circuit being constituted, forexample, by an indicator light mounted on the dashboard of the vehicle,or by an audible warning device. Between the plug 15 and the sleeve 14,there is provided a resilient and watertight sheath 16 having one end 17secured to the plug 15 and having its other end 18 preferably overlyingat least a portion of the sleeve 14. The purpose of the sheath 16 is toexert a force on the sleeve 14 that is directed towards the pellet 6 sothat the end 19 of the sleeve 14 which is remote from the plug 15 tendsto be received in the recess 13 of the pellet 6.

As can be seen in FIGS. 1 and 2, and in FIGS. 5A, 5B and 5C, the lining2 has a first blind bore 20 which opens out in the braking face 4, andwhose end wall 21 is advantageously constituted by the support plate 3.A second bore 22 connects the first bore 20 to the edge 23 of the lining3. This second bore 22 opens out into the first bore 20 in the vicinityof its end wall 21. The lining 2 also includes a slot 24 which extendsbetween the first bore 20, the second bore 22, the edge 23, and thebraking face 4. It optionally includes other slots 25 for facilitatingcooling of the lining 2, should that be considered necessary given theuse for which pad 1 is intended.

The dimensions of the first bore 20 are designed so that the pellet 6 iscapable of passing into said first bore 20.

The diameter of the second bore 22 is substantially equal to thediameter of the sleeve 14 covered in its resilient sheath 16. The widthof the slot 24 is less than the diameter of the sleeve 14 and slightlygreater than the thickness of the conductor wire 10.

The wear indicator 5 is mounted on the brake pad 1 in the manner shownin FIGS. 5A, 5B, and 5C.

As can be seen in FIG. 5A, the operator presents the pellet 6 to theorifice of the first bore 20, manually pulling the sleeve 14 away fromthe pellet 6 by exerting a force F on the sleeve 14 that compensates theopposing force exerted by the resilient sheath 16. The lengths of wire12a and 12b are placed facing the slot 24. Thereafter, it suffices todisplace the indicator 5 in the direction of arrow D.

Once the pellet has been placed in the end 21 of the first bore 20, asshown in FIG. 5B, the lengths of wire 12a and 12b are substantially inthe centre of the second bore 22. To lock the pellet 6 in the first bore20, the operator then releases the sleeve 14. The sheath 16 then exertsa force F on the sleeve 14, which force is directed towards the pellet6. The sleeve 14 penetrates automatically into the second bore 22. Wherenecessary, the operator may apply additional force to the sleeve 14 bypressing it with a finger so as to cause it to press against the pellet6.

FIG. 5C shows the sleeve 14 locked in,he second bore 22 at the end ofthe assembly operation. The end 19 of the sleeve 14 is received in therecess 13.

The wear indicator 5 operates as follows: when, because of wear, thelining 2 is of a thickness that is less than the thickness of the pellet6, the rotary part of the brake wears away the material of the pellet.There comes a moment when the loop 9 is itself subjected to wear, sothat conductor wire 10 is then electrically connected to the rotary partwhile braking is taking place. Since the rotary part is connected toground, the electrical indicator circuit is closed.

When changing brake pads 1, it is possible to reuse the wear indicator 5of the invention if its pellet 6 has not itself been worn. Under suchcircumstances, it suffices to extract the sleeve 14 from the second bore22 and to withdraw the pellet 6 from the first bore by causing thelengths of wire 12a and 12b to pass through the slot 24.

The through hole 26 in the support plate 3 serves to pass the lead ofthe indicator 5. The holes 27 serve to mount the brake pad on the brakecalliper.

In the embodiment described above, the end 18 of the resilient sheath 16covers at least a portion of the sleeve 14. Clearly the end 18 of thesheath 16 could merely press against the outer end of the sleeve 14.Similarly, the loop 9 could be replaced by a terminal embedded in themass of the pellet 6, with the lengths of wire 12a and 12b beingelectrically connected thereto. Under such circumstances, the pellet 6no longer has grooves 8 and the recess 13 may be omitted. Similarly, theholes 26 and 27 of the support plate 3 are not essential.

In a variant embodiment shown in FIGS. 6, the pellet is provided with aradial rod 30 whose diameter is not greater than the thickness of theslot 24. The pellet 6 and the radial rod 30 are formed by overmouldingon the loop 9 and on the two lengths of wire 12a and 12b that extend theloop 9. When the pellet 6 is disposed in the end 21 of the first bore20, the radial rod 30 is centred in the second bore 22. In thisembodiment, the sleeve 14 may advantageously be replaced by the end 18of the resilient sheath 16 which is received in the second bore 22,holding the radial rod 30 captive. This disposition makes it possible tohold the pellet 6 accurately in the end 21 of the first bore 20.

We claim:
 1. A brake pad for a vehicle brake, the pad comprising afriction lining (2) and a wear indicator (5) fixed by fixing means, saidindicator (5) comprising a body (6) of insulating material and anelectrical conductor (10) designed to be connected to an electricalindicator circuit, a portion (9) of said conductor (10) being disposedin said body (6) in such a manner that it is itself worn by a rotarypart of the brake once the friction lining (2) has been reduced to athickness of less than a predetermined value, the brake pad beingcharacterised by the fact that the body (6) is shaped to be received inthe bottom of a first blind bore (20) formed in the friction lining (2)and opening out into the braking face (4) of said lining, by the factthat the means for fixing the indicator (5) on said lining (2) comprisea rigid sleeve (14) slidably mounted on the electrical conductor (10) inthe vicinity of said body (6) and suitable for being received in asecond bore (22) formed in said lining (2) and opening out into saidfirst bore (20) and to one of the edges (23) of the lining (2), and bythe fact that a slot (24) is provided in the friction lining to pass theelectrical conductor (10) during installation of the wear indicator (5)on said lining (2), said slot (24) being narrower than the diameter ofthe sleeve (14) and extending between said first bore (20), said secondbore (22), said edge (23), and said braking face (4).
 2. A brake padaccording to claim 1, characterised by the fact that means are providedfor holding the sleeve in the second bore (22).
 3. A brake pad accordingto claim 2, characterised by the fact that the free end of theelectrical conductor (10) includes a plug (15) for connection to theelectrical indicator circuit, and by the fact that the means for holdingthe sleeve (14) in the second bore (22) comprise a resilient sheath (16)capable of sliding over the electrical conductor and of exerting on saidsleeve (14) a force (F) that is directed towards the body (6).
 4. Abrake pad according to claim 3, characterised by the fact that sleeve(14) is inserted in one end of said resilient sheath (16).
 5. A brakepad according to claim 1, characterised by the fact that the body (6) isin the form of a pellet (6).
 6. A brake pad according to claim 5,characterised by the fact that the pellet (6) has an annular groove (8)in its edge (7), and by the fact that the electrical conductor (20) isan insulated conductor wire forming a loop that is received in saidgroove (8).
 7. A brake pad according to claim 6, characterised by thefact that the pellet (6) includes, in its edge (7), a recess (13)adapted to receive the inner end (19) of the sleeve (14).
 8. A brake padaccording to claim 1, characterised by the fact that the body is in theform of a pellet (6) provided with a radial rod (30) whose diameter isno greater than the thickness of the slot (24), said pellet (6) and saidrod (30) being formed by being moulded over a portion (9, 12a, 12b) ofthe electrical conductor (10).
 9. A brake pad according to claim 8,characterised by the fact that the sleeve is constituted by the end (18)of a resilient sheath (16).